Yes, a lot. It’s a combination of many small and some quite big.
I was able to narrow my issue a bit, ruling out seafile-server / nginx problems, as i’m able to download really fast (~99MB/s) from a seafile-client in linux server (with HDDs not SSDs) in same Gb lan.
From my macos laptop (100MB or 300MB connections), Seadrive in SSD goes also really fast, being the limit the bandwidth. In nginx log, fast continuous requests can be seen. On the other side, Seafile client uses an usb-c sata HDD with speeds higher than 100MB/s and HFS+ format. Here is where download is so slow, even in nginx log it can be seen that slowness in requests, going slowly one by one, and with download file list taking a lot of time and repeating continuously.
That way, the bottleneck seemed to me to be related to that usb-c HDD, but if I make a full download of library in the same Gb lan linux server, and then, in laptop, I use rsync or resilio sync to move that library files from the server to the macos laptop usb-c HDD, things are fast again, with home bandwidth being the limit. So, there is some combination of things here that make seafile sync unable to sync in a reasonable amount of time, as it stays a lot of time with minimal network transmission